A facile approach to covalently functionalized carbon nanotubes with biocompatible polymer

Biocompatible poly(l-lactic acid) (PLA) was successfully covalently grafted onto the convex surfaces and tips of the multi-walled carbon nanotubes (MWNTs) by one step based on in situ polycondensation of the commercially available l-lactic acid monomers. The functional groups in the carboxylic multi-walled carbon nanotubes (MWNT-COOH) showed active enough for participating the polycondensation of l-lactic acid. The resulting PLA-grafted-MWNTs were characterized with Raman spectroscopy, Fourier-transform IR (FTIR), UV–vis, 1H NMR, thermogravimetric analyses (TGA) and transmission electron microscopy (TEM). Raman, FTIR and 1H NMR spectroscopies revealed that the PLA was covalently attached to the MWNT. TGA showed that the grafted PLA content could be controlled by the reaction time. The core/shell structures with MWNT as the “hard” core and the PLA polymer layer as the “soft” shell can be clearly seen through HRTEM.